The immediate objectives of this project are to apply the tissue culture techniques to the study of the fundamental mechanisms of cell infection and transformation by the mouse mammary tumor virus (MuMTV). Cat kidney cells and mink lung cells which have shown a remarkable susceptibility to that virus in vitro are used to analyze viral synthesis. Efforts are particularly directed towards the development of a titration assay using immunofluorescence or possibly a plague-forming system. The susceptibility of epithelial cells from a variety of other species is also investigated. Further attempts are being made to obtain a cell line from primary human breast tumors to compare its cell surface antigens with those of mouse mammary tumors and with surface antigens of MuMTV-infected cat and mink cells. BIBLIOGRAPHIC REFERENCES: Lasfargues, E.Y., A. Dion, J.C. Lasfargues, and D.H. Moore. Effect of dexamethasone on the mouse mammary tumor virus grown in cat kidney cells. Proc. Am. Assoc. Cancer Res. 16:28 (lll), 1975. Lasfargues, E.Y., J.C. Lasfargues, A. Dion, A.E. Greene, and D.H. Moore. Experimental infection of a cat kidney cell line with the mouse mammary tumor virus. Cancer Research 36:67-72, 1976.